diff --git a/src/s5p/pool.py b/src/s5p/pool.py
index cca803d..0d099fb 100644
--- a/src/s5p/pool.py
+++ b/src/s5p/pool.py
@@ -66,21 +66,21 @@ class ProxyPool:
     # -- public interface ----------------------------------------------------
 
     async def start(self) -> None:
-        """Load state, fetch sources, run initial health test, start loops."""
+        """Load state, fetch sources, start background loops.
+
+        On warm start (state file has alive proxies), the pool begins
+        serving immediately using cached state and defers all health
+        testing to background tasks.  On cold start, a full health
+        test runs before returning so the caller has live proxies.
+        """
         self._load_state()
-        warm_keys = list(self._alive_keys)
+        warm = bool(self._alive_keys)
         await self._fetch_all_sources()
 
-        if warm_keys:
-            # warm start: quick-test previously-alive proxies first
-            valid_keys = [k for k in warm_keys if k in self._proxies]
-            if valid_keys:
-                await self._run_health_tests(keys=valid_keys)
-                self._save_state()
-                self._tasks.append(asyncio.create_task(self._deferred_full_test()))
-            else:
-                await self._run_health_tests()
-                self._save_state()
+        if warm:
+            # trust persisted alive state, verify in background
+            self._save_state()
+            self._tasks.append(asyncio.create_task(self._deferred_full_test()))
         else:
             # cold start: test everything before serving
             await self._run_health_tests()